Generally, heavy-weight detergents have a composition basically comprising a surfactant, an alkalizing agent, and a metal ion capturing agent, wherein the surfactant is added to dissolve dirt stains, the alkalizing agent is added to accelerate the elution of fatty acids which are present in sebum dirt stains, the swelling of fibers, and dispersion of the dirt stains, and the metal ion capturing agent is added to remove water hardness-increasing components, such as calcium and magnesium ions. These detergents may optionally contain other additives such as detergent aids.
More specifically, anionic surfactants including alkylbenzenesulfonates and alkylsulfates, and nonionic surfactants typically exemplified by polyoxyethylene alkyl ethers may be mainly used for base materials of the surfactants. Alkali metal carbonates and alkali metal silicates may be generally used for base materials of the alkalizing agents. Phosphates, aluminosilicates, and polycarboxylates may be generally used for base materials of the metal ion capturing agents. Among these base materials, the phosphorus-containing compounds typically exemplified by tripolyphosphates have been convenient base materials because they are able to act as alkalizing agents and also have excellent metal ion capturing ability. However, the use of tripolyphosphates, etc. may give causes to eutrophication in rivers, lakes, and marshes. Therefore, phosphorus-free detergents using aluminosilicates typically represented by 4A-type ZEOLITE are at present mainly used.
The compositional changes are made, owing to the fact that the aluminosilicates do not have as high a level of an alkalizing ability as the tripolyphosphates, and the deficient alkalizing ability is supplemented by increasing the amounts of the alkali metal carbonates conventionally supplemented as dissolution aids or by increasing the amounts of amorphous alkali metal silicates conventionally added to increase the mechanical strength of the detergent granules or added with an intention to allow it to act as anticorrosive agents.
Crystalline alkali metal silicates disclosed in Japanese Patent Laid-Open Nos. 5-184946 and 60-227895, of which the disclosure is incorporated herein by reference, have not only an alkalizing ability at a level equivalent to or higher than that of the conventional amorphous alkali metal silicates, but also a good metal ion capturing ability, so that they are most closely paid attention as an alternative base material. There are numerous publications disclosing detergent compositions using these crystalline alkali metal silicates, including Japanese Patent Unexamined Publication Nos. 6-507197, 6-500141, and 6-502445 and Japanese Patent Laid-Open No. 7-53992, of which the disclosure is incorporated herein by reference.
Also, for the purposes of controlling pHs and capturing metal ions, there have been proposed in a number of patent applications to include an acid ingredient in the detergent compositions.
For instance, Japanese Patent Laid-Open No. 3-100100, of which the disclosure is incorporated herein by reference, discloses an invention concerning a dishwashing agent comprising a combination of a layered, crystalline alkali metal silicate and a proton donor. However, the purpose of the invention disclosed herein is to reduce the irritation against skin and eyes to which the person in use may be subjected during dishwashing by lowering the pH of the washing liquid, not to improve the detergency against the sebum dirt stains by adjusting an initial rise of the pH at initial washing.
In addition, Japanese Patent Unexamined Publication No. 6-507197, of which the disclosure is incorporated herein by reference, discloses an invention concerning a solid washing detergent composition comprising a uniform mixture of a crystalline alkali metal silicate and a solid water-soluble ionic substance, wherein the crystalline alkali metal silicate and the solid water-soluble ionic substance are contained in particular proportions. Here, it is suggested that both the crystalline alkali metal silicate and the polycarboxylic acid are formulated in the detergent composition. However, the purpose of the invention disclosed herein is to avoid damages to fibers of wool, etc. which are sensitive to alkalis, the damages being caused by a local increase in the pH when the detergent granules containing the crystalline alkali metal silicate are dissolved on clothes. In order to avoid such a problem, the pH is controlled by uniformly blending the crystalline alkali metal silicate with the water-soluble substance capable of forming ions in the same granule in the publication. Also, in this technique, the technical idea that the amount of the acidic ingredient present in a separate granule is not lowered until the instance of introducing detergents is not disclosed, as will be described in detail later, and the acid may be present in the form of salts. Therefore, it does not suggest that remarkable improvements in detergency are achieved by adjusting an initial rise of the pH at the beginning of washing by formulating the acidic ingredient in a granule different from a granule containing the crystalline alkali metal silicate.
Further, Japanese Patent Laid-Open No. 7-48597, of which the disclosure is incorporated herein by reference, discloses an invention concerning a detergent containing a surfactant, a builder, and a polyglycol diacid in particular proportions. However, the invention disclosed herein does not teach that the polyglycol diacid is not formulated in a separate granule from a granule containing the crystalline alkali metal silicate, and the acidic substance is simply added for the purpose of capturing metal ions.
Incidentally, the sebum dirt stains derived from human bodies contain in its most part fatty acids. The most significant effect of the alkalizing agent is to dissolve dirt stains by saponifying the fatty acids in the sebum dirt stains. However, in the presence of the water hardness-increasing components of calcium or magnesium ions in the washing liquid, these components form a scum with the fatty acids, so that its solubility is lowered, thereby preventing the dissolution or dispersion in the dirt-containing washing liquid. In particular, the present inventors have found that higher the degree of alkalization, faster the scum-formation rate, noting that sufficient washing performance cannot be exhibited by the conventional methods when designing detergent compositions using the crystalline alkali metal silicate having a high degree of alkalization.
Accordingly, an object of the present invention is to provide a granular detergent composition for clothes washing with an even superior washing power.
These and other objects of the present invention will be apparent from the following description.